4817399 Maybe because she can't bring herself to settle down and raise a family, knowing that they'd be subject to public scrutiny and political attacks?

4817399 I like the SilFoe approach myself.

I like to think that it's because she doesn't want one knowing that she'll have to watch them grow old and die, while she would not. The worst fate of any parent is to outlive their children.
That's one of my most logical reasonings for Momlestia and Spike. She adopted him possibly because he might actually live as long as she would.

4817399 Because since alicorns are beings with higher outlooks on morality, they lack the urges to reproduce except to keep the population at a stable level in the galaxy.

4817399 okay first theory alicorns are infertile or atleast conceiving is difficult. Second theory she has but they all were mortal and she out lived them, or she has kept them and their descendents a secret.
Third theory she just hasn't found the right mare/stallion or prior betrayal makes her wary.
Fourth theory alicorn reproduction is alicorn ascension and happens once the centennial or millennial when an alicorn goes into heat and the ensuing mating makes the mate an alicorn. Technically meaning cadance and twi are celestia's foals( you can thank field notes on alicorn reproductive behaviour for this one)

There a different from not being told about them and she not having them.

Perhaps she only goes into estrus once every five-hundred years or so, and the foals in no longer among the living?

Has she forgot about Spike?

4817399

Maybe Alicorns can only reproduce within their own species.

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Maybe she has and we don't know about them.